The present invention relates to a planetary roller gear drive that converts a relative rotation between a spindle nut and a threaded spindle into a relative translational displacement between the spindle nut and threaded spindle.
From DE 102009040606 A1, a planetary roller gear drive is known that is provided with a plurality of planets that are arranged distributed around the periphery and are in rolling engagement with the threaded spindle and the spindle nut, wherein the threaded spindle has a plurality of helical-shaped windings wound around the spindle axis of at least one thread groove. The spindle nut is provided with a nut-side profile on its inner periphery, wherein the planet-side profile of the planets is in rolling engagement with the nut-side profile. The planet-side profile is formed by annular, closed grooves that are arranged perpendicular to the planet axis. The planets revolve on planetary orbits that are arranged perpendicular to the spindle axis.
For planetary roller gear drives, the transmission ratio between the spindle nut and the threaded spindle is defined by the pitch of the thread groove on the threaded spindle, also by the rolling circle diameter of the threaded spindle and the spindle nut, and also by the rolling circle diameter of the planet, wherein often stepped planets with two different rolling diameters are used, a larger rolling diameter for the rolling engagement with the threaded spindle and a smaller rolling diameter for the rolling engagement with the spindle nut. In the case of stepped planets, with respect to the length of the planets, approximately one half the length of the planet is in rolling engagement with the spindle nut and the other half of the length is in rolling engagement with the threaded spindle.
If planetary roller gear drives with high load ratings and large spindle diameters are used, load-bearing lengths on the threaded spindle and on the spindle nut of, for example, 100 mm to 150 mm could be required, so that, in the case of stepped planets, lengths of up to 300 mm are needed. Such planetary roller gear drives are expensive to produce.